The present invention generally relates to tanks for collecting waste liquid, and more particularly to collection tanks used in vacuum drainage systems.
Health and Environmental agencies require waste water to be collected and directed to a proper receptacle, such as a municipal sewer or private septic tank. The term xe2x80x9cwaste waterxe2x80x9d as used herein includes used or dirty process water (known as gray water), and sewage water (commonly referred to as black water). Gray water may be generated from a variety of different operations. In a grocery store, for example, water is used in deli, food service, and floral departments for cleaning, maintenance, and other purposes. Refrigerated display cases generate additional process water from condensate and defrost procedures. The waste water generated from these various sources must be collected and transported to the proper receptacle.
In the past, conventional gravity drainage piping has been used to collect and transport waste water. Gravity drainage systems use collection points located below the waste water source which feed into drainage pipes leading to a sewer line. The piping in such systems must be continuously sloped so that the waste water flows all the way to the sewer line. As a result, pipes for gravity drainage systems are often laid in or underneath the concrete pad supporting the facility. This process not only requires significant amounts of additional plumbing work, but also complicates changes in facility layout, which would require portions of the concrete pad to be ripped up to expose drainage channels.
More recently, vacuum drainage systems have been used to collect and transport waste water. A vacuum drainage system typically comprises a collection drain located under each waste water source, each collection drain leading to a common drain pipe. The drain pipe is connected to a collection tank which is in fluid communication with a pump. The pump creates negative pressure in the tank and drain pipe to thereby pull liquid through the drain pipe and into the tank. The tank has a drain that is typically positioned over a sewer line to allow the tank to be emptied.
It will be appreciated that the tanks used in vacuum drainage systems must be large enough to hold a substantial volume of liquid while withstanding a continuous external pressure without buckling. For example, collection tanks are typically sized to house approximately 20-100 gallons of liquid. The side walls of such tanks are often cylindrical, and have a diameter of approximately 17 to 60xe2x80x3. Furthermore, conventional vacuum drainage systems often generate continuous negative pressures of up to 25xe2x80x3 Hg or more.
As a result, previous tanks used in vacuum drainage systems have been formed of steel. Steel tanks, however, are overly costly to fabricate. In addition, steel is overly heavy for certain tank applications. Furthermore, steel quickly conducts outside temperature to the liquid contained therein and, therefore, is not suitable for certain applications in which the stored liquid is intended to maintain an elevated temperature. Still further, steel requires expensive treatment to resist corrosion or the life of the tank will be significantly shortened.
In accordance with certain aspects of the present invention, a vacuum waste tank is provided for use in a vacuum drainage system having a vacuum drainage pipe and a vacuum source fluidly communicating with the tank. The tank comprises a cylindrical side wall, first and second end caps attached to opposite ends of the side wall to form an enclosed chamber, a vacuum intake adapted for fluid communication with the vacuum source, and a drain outlet. The side wall and end caps are formed of a thermoplastic material having a flexural modulus of at least 175,000 psi.
The side wall of the tank may be formed with ribs projecting substantially outwardly. The ribs may be formed to resist buckling under an external pressure load on the tank of 25xe2x80x3 Hg. In that regard, the ribs preferably have a substantially rectangular cross-section formed by radially outwardly extending upper and lower flanges connected at outside edges by a cylindrical side member. The tank may have a diameter of approximately 17 to 28 inches. In a most preferred embodiment, the thermoplastic material is polypropylene.
In accordance with additional aspects of the present invention, a vacuum waste tank is provided comprising a cylindrical side wall, first and second end caps attached to opposite ends of the side wall to form an enclosed chamber, a vacuum intake, a waste water intake, a drain, and a plurality of ribs extending about a circumference of the side wall and spaced along a length of the side wall by a spaced distance. The side wall and end caps are formed of a thermoplastic material capable of resisting a continuous external pressure loading resulting from a negative pressure in the chamber of approximately 10 to 25 inches Hg.
Other features and advantages are inherent in the apparatus claimed and disclosed or will become apparent to those skilled in the art from the following detailed description and its accompanying drawings.